Effects of the novel immunosuppressant FTY720 in a murine rheumatoid arthritis model

We investigated the effects and mechanisms by which FTY720 (FTY) inhibits arthritis development in the SKG mouse rheumatoid arthritis (RA) model. FTY (1 mg/kg/day) administration suppressed the progression of laminarin-induced arthritis in SKG mice. FTY treatment decreased IL-6 and TNF-α expression in synovial fibroblast cells and the number of inflammatory cells overall. Bone destruction was also suppressed by treatment with FTY. The numbers of CD4+ and CD8+ T cells were significantly increased in the thymus and decreased in the spleen in FTY-treated SKG mice. FTY enhanced IL-4 production by CD4+ T cells stimulated by allogeneic spleen cells and inhibited prostaglandin E2 (PGE2) production by a TNF-α-stimulated synovial fibroblast cell line. These results indicate that FTY can inhibit arthritis in SKG mice via sequestration of autoimmune CD4+ T cells in the thymus, enhancement of Th2 immune responses, and inhibition of PGE2 production by synovial cells.